Self-Contained Hydraulic Actuator System

ABSTRACT

The hydraulic linear actuator system of the present invention includes a pump that is configured to rotate in a single direction at a substantially constant velocity. Both the direction and flow rate of fluid through the system is controlled by adjusting the positional relationship between the stator and the rotor of the pump. This positional relationship is adjustable between a forward flow state, a non-flow state and a reverse flow state. The hydraulic linear actuator is responsive to the flow of fluid through the system so as to be displaced in a first direction by the forward flow state of the pump and in a second direction by the reverse flow state of the pump.

This is a Continuation-In-Part of, and therefore claims priority from,application Ser. No. 11/186,946 filed 22 Jul. 2005.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to self-contained actuator systems and, inparticular, it concerns a self-contained hydraulic linear actuatorsystem having a pump, the pumping assembly of which is adjustable so asto control the speed and direction of the fluid flow through the systemand a linear actuator responsive to the fluid flow.

Self-contained hydraulic actuator systems having closed hydraulicsystems incorporating bi-directional pumps are known in the art.Heretofore, these systems required bi-directional motors to drive thepump. Therefore, the speed and direction of pump rotation, and thusfluid flow through the system, is the direct result of the movement ofthe motor driving the pump. The motors best suited for this purpose areelectrical servomotors, which provide the ability to change speed anddirection quickly as required. This is particularly relevant in thefield of motion simulation.

There are a number of drawbacks associated with the use of servomotorsto drive bi-directional pumps. One major drawback is that bi-directionalservomotors are expensive since they must be built to perform, andwithstand the rigors of, substantially instantaneous changes of speedand/or direction numerous times during the performance of a task.

There is therefore a need for a self-contained hydraulic linear actuatorsystem having a pump, the pumping assembly of which is adjustable so asto control the speed and direction of the fluid flow through the systemand a linear actuator responsive to the fluid flow. It would beadvantageous if the system included a closed hydraulic system.

SUMMARY OF THE INVENTION

The present invention is a self-contained hydraulic linear actuatorsystem having a pump, the pumping assembly of which is adjustable so asto control the speed and direction of the fluid flow through the systemand a linear actuator responsive to the fluid flow.

According to a further teaching of the present invention, aself-contained hydraulic actuator system comprising; a) a drive motorconfigured to rotate at a substantially constant velocity; b) ahydraulic pump driven by the drive motor; c) a hydraulic linear actuatorin fluid communication with the hydraulic pump so as to be actuated in afirst direction by a forward flow state and in a second direction by areverse flow state; d) a control system associated with the hydraulicpump, the control system configured to control adjustment of thehydraulic pump between the forward flow state, a non-flow state and thereverse flow state, and the control system includes a bi-directionalmotor such that a speed and direction of the adjustment is affected bythe bi-directional motor; and e) a positioning system configures toprovide positional information regarding the hydraulic linear actuator.

According to a further teaching of the present invention, the hydraulicpump includes a controllably variable pumping assembly such that theadjustments includes a variation of the controllably variable pumpingassembly.

According to a further teaching of the present invention, the hydraulicpump includes a stator and a rotor deployed within the stator and thevariation of the controllably variable pumping assembly includesadjusting the positional relationship between the stator and the rotor.

According to a further teaching of the present invention, the hydraulicpump is a vane pump.

According to a further teaching of the present invention, thepositioning system includes a position feedback system configured toprovide position information regarding the hydraulic linear actuator.

According to a further teaching of the present invention, the positionfeedback system includes at least one of an optical encoder and a linearpotentiometer associated with the actuator.

According to a further teaching of the present invention, the fluidcommunication between the hydraulic pump and the actuator is via aclosed hydraulic system.

According to a further teaching of the present invention, there is alsoprovided: a) a fluid expansion reservoir; and b) a valve configurationconfigured so as to maintain fluid communication between the fluidexpansion reservoir and a downstream port of the hydraulic pump.

According to a further teaching of the present invention, the hydraulicpump is configured with first and second ports, and the first and secondports alternately act as upstream and downstream ports such that whenthe first port acts as the upstream port the second port acts as thedownstream port, and when the first port acts as the downstream port thesecond port acts as the upstream port, therefore, the valveconfiguration maintains the fluid communication between the fluidexpansion reservoir and one of the first and second ports, dependent onwhich of the first and second ports is acting as the downstream port.

According to a further teaching of the present invention, the fluidexpansion reservoir is not vented.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a side elevation of a preferred embodiment of a self-containedhydraulic linear actuator system constructed and operative according tothe teachings of the present invention;

FIG. 2 is a top elevation of the embodiment of FIG. 1;

FIG. 3 is a cross-sectional view of the embodiment of FIG. 1 taken alongline A-A, showing the stator adjusted toward the left side of the pumphousing;

FIG. 4 is cross-sectional view of the embodiment of FIG. 1 taken alongline B-B, showing the stator adjusted toward the left side of the pumphousing;

FIG. 5 is cross-sectional view of the embodiment of FIG. 1 taken alongline B-B, showing the stator adjusted toward the right side of the pumphousing;

FIG. 6 is cross-sectional view of the embodiment of FIG. 1 taken alongline B-B, showing the stator adjusted to the neutral position;

FIG. 7 is a schematic of a preferred hydraulic circuit constructed andoperative according to the teachings of the present invention, showingthe shuttle valve deployed in a fluid supply state;

FIG. 8 is a schematic of a preferred hydraulic circuit constructed andoperative according to the teachings of the present invention, showingthe shuttle valve deployed in a fluid reception state; and

FIG. 9 is a block diagram of a preferred embodiment of a control systemfor the linear actuator constructed and operative according to theteachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a self-contained hydraulic linear actuatorsystem having a pump, the pumping assembly of which is adjustable so asto control the speed and direction of the fluid flow through the systemand a linear actuator responsive to the fluid flow.

The principles and operation of a self-contained hydraulic linearactuator system according to the present invention may be betterunderstood with reference to the drawings and the accompanyingdescription.

By way of introduction, the hydraulic linear actuator system of thepresent invention includes a pump that is configured to rotate in asingle direction at a substantially constant velocity. Therefore, thedrive motor that drives the pump can be a single direction constantvelocity motor such as is known in the art, rather than a bi-directionalvariable speed servomotor. This gives the hydraulic linear actuatorsystem of the present invention a substantial cost advantage oversystems that employ a more expensive bi-directional variable speedservomotor.

Both the direction and flow rate of fluid through the system iscontrolled by adjusting the configuration of the pump, which isadjustable between a forward flow state, a neutral non-flow state and areverse flow state. The hydraulic linear actuator is responsive to theflow of fluid through the system so as to be displaced in a firstdirection by the forward flow state of the pump and in a seconddirection by the reverse flow state of the pump.

It should be noted that the use of the terms “clockwise,”“counter-clockwise,” “left” and “right”, are used herein with referenceto direction as seen in the drawings.

Referring now to the drawings, FIGS. 1 and 2 illustrate side and topelevations, respectively, of the exterior of a preferred embodiment ofthe hydraulic linear actuator system 2 of the present invention. Seenhere are the drive motor 4, the stepper motor housing 6 that houses thestepper motor that affects adjustment of the configuration of the pump,as will be discussed below, the linear actuator 8, and the pump 20.Attached to the pump 20 is the fluid expansion reservoir 40, which willbe discussed below.

The drive motor is preferably an AC electric motor. However, it shouldbe noted that substantially any drive device such as, but not limitedto, DC electric motors, and internal combustion engines, may be used todrive the pump.

The linear actuator 8 may be a hydraulic cylinder and piston actuator,as is illustrated herein, in which the actuator cylinder 10 is rigidlyattached to the pump 20 via the actuator attachment extension 12 of thepump 20 that is configured with fluid passageways which provide fluidcommunication between the pump 20 and the actuator cylinder 10. It willbe appreciated that the actuator 8 need not be attached to the pump 20and that fluid communication may be provided by substantially any methodknown in the art such as, but not limited to, hoses, tubes, pipes, andany other suitable fluid conduit. It will also be appreciated thatsubstantially any hydraulically driven device may be associated with thepump 20 of the present invention.

In a preferred embodiment described herein, the pump 20 illustrated is arotary vane pump configured with a controllably variable pumpingassembly. It should be noted, however, that the principles of thepresent invention may be applied to equal advantage to piston pumps aswell. As seen in FIGS. 3-6 the variable pumping assembly, which isdeployed within the pump housing 22, includes a displaceable stator 24and a rotor 26 with a plurality of vanes 28 deployed within the stator24. The stator 24 is configured so as to pivot about the pivot shaft 30,while the rotor 26 rotates in a static position. Therefore, thepositional relationship between the stator 24 and the rotor 26 may beadjusted. As the positional relationship between the stator 24 and therotor 26 is adjusted, the position of the working pump volume 32 withinthe stator 24 is varied, as is illustrated clearly in FIGS. 4-6. Thisalso varies the positional relationship of the working pump volume 32 tothe inlet/outlet ports 34 and 36. The ports 34 and 36 are referred toherein as inlet/outlet ports because their role changes with thedirection of fluid flow through the pump. With regard to the discussionherein, the rotor is considered to be rotating in a clockwise direction(see arrow 38).

In FIG. 4, the stator 24 is displaced to the far left and the majorityof the working pump volume 32 is to the left of the rotor 26. Therefore,fluid is drawn into the working pump volume 32 during an expansionstroke, through inlet/outlet port 36, which is now acting as the inletport. As pump comes to an exhaust stroke the fluid is forced out of theworking pump volume 32 through inlet/outlet port 34, which is now actingas the outlet port.

In FIG. 5, the stator 24 is substantially centrally deployed and theworking pump volume 32 is substantially evenly distributed around therotor 26. Therefore, there are neither expansion nor exhaust strokes andsubstantially no fluid is drawn in, or forced out, of the working pumpvolume 32 through either of the inlet/outlet ports 34 and 36. In this“neutral” position, a non-flow state is achieved within the hydraulicsystem.

In FIG. 6, the stator 24 is displaced to the far right and the majorityof the working pump volume 32 is to the right of the rotor 26.Therefore, fluid is drawn into the working pump volume 32 during anexpansion stroke, through inlet/outlet port 34, which is now acting asthe inlet port. As pump comes to an exhaust stroke the fluid is forcedout of the working pump volume 32 through inlet/outlet port 36, which isnow acting as the outlet port.

Thusly configured, the speed and direction of fluid flow through thepump 20, and therefore through the system, is controlled by adjustingthe positional relationship between the stator 24 and the rotor 26. Dueto the location of the inlet/outlet ports, when the stator 24 ispositioned in a central, “neutral” position (FIG. 5), a non-flow stateis achieved within the hydraulic system. As the stator 24 is displacedaway from the neutral position in a first direction, for example to theleft (FIG. 4), a forward flow state is achieved. As the stator 24 isdisplaced away from the neutral position in a second direction, forexample to the right (FIG. 6), a reverse flow state is achieved. It willbe appreciated that the further away from the neutral position thestator is displaced, the more fluid will be moved though the pump 20.The amount of fluid moving through the pump affects the speed anddistance of actuator displacement. It will be understood that directionof rotor rotation, and which direction of fluid flow is considered toforward and reverse flow states are considered to be designconsiderations, and examples used herein are not to be considered aslimitations.

Adjustment of the position of stator 24 is affected by a bi-directionalstepper motor (not shown here) that is housed within the stepper motorhousing 6 and controlled by a control system that includes the positioncontroller 64. The stepper motor drives spur 60, which interacts withspur gear section 62 that extends from the stator 24. Configured thus,speed and direction of rotation of the stepper motor affects the speedand direction of stator 24 displacement. As illustrated herein, rotationof the stepper motor in a clockwise direction will displace the stator24 to the left and counter-clockwise rotation will displace the stator24 to the right. It will be appreciated that while the preferredembodiment of the present invention described herein refers to the useof a stepper motor to adjust the position of stator 24, this is notintended as a limitation to the scope of the present invention.Therefore, variant embodiments in which adjustment of the position ofstator 24 is directly affected by another drive device such as, but notlimited to, a bi-directional motor, or a unidirectional motor inconjunction with a direction changeable gear train.

The speed and rotational direction of the stepper motor is controlled bythe position controller 64 as illustrated in FIG. 9. In this embodimentof the present invention, when the position controller receives acommand to bring the hydraulic linear actuator 8 to a desired position,the current position of the hydraulic linear actuator 8 is determinedbased on feedback from the feedback system that includes the opticalencoder 70, which is associated with the hydraulic linear actuator 8. Itshould be noted that feedback regarding the position of the hydrauliclinear actuator 8 may be supplied by a linear potentiometer in insteadof, or in addition to, the optical encoder. Based on the currentposition of the hydraulic linear actuator 8 and the speed at which thechange of position is to be affected, the rotational direction andnumber of steps the stepper motor 66 must take, and the rate at whichthe step must be taken is determined. The pulse generator included inthe stepper motor driver 68 then delivers the appropriate pulses, at theappropriate rate, thereby causing the stepper motor 66 to turn thenecessary amount in order to bring the stator 24 to the requiredposition to affect the desired position of the hydraulic linear actuator8. It will be appreciated that in embodiments of the present inventionwhich have remote actuators, that is, actuators that are not directlyattached to the pump 20, the control system may be configured with COMports to provide external connection access to the control system.

It is noteworthy that, unlike systems of prior art that utilize steppermotors and track position bases on the number and direction of steptaken, the present invention uses the features of the stepper motor 66solely for the purpose of controlling the direction and amount of stator24 displacement and the speed at which the displacement occurs. Theposition of the hydraulic linear actuator 8 is monitored by apositioning system that includes the encoder 66 which provides positionfeedback to the position controller 64. This provides a more accurateindication of the true position of the hydraulic linear actuator 8,since the rotation of the stepper motor 66 is not directly related tothe displacement of the hydraulic linear actuator 8. Rather, rotation ofthe stepper motor 66 is directly related to the position of the stator24 which in turn affect displacement of the hydraulic linear actuator 8.

It will be appreciated that the use of a hydraulic cylinder and pistonactuator in a closed hydraulic system present the problem of the volumedifferential between the two sides of the piston since the one sideincludes the actuator rod 14 (FIGS. 1 and 2). One way to solve thisproblem is the inclusion of a fluid expansion reservoir 40 and a valve42 to control the flow of fluid into and out of the fluid expansionreservoir 40. Another solution could include configuring the hydrauliclinear actuator 8 with two actuator rods 14, one extending to each sideof the piston, thereby effectively eliminating the volume differentialbetween the two sides.

As described above, the direction of fluid flow through the hydraulicpump of the present invention is controlled by displacement of thestator 24. Therefore, as illustrated in the schematic views of FIGS. 7and 8, the inlet and outlet ports of the pump 20 alternately act asupstream and downstream ports such that when the first port 44 acts asthe upstream port the second port 46 acts as the downstream port, andwhen the first port 44 acts as the downstream port the second port 46acts as the upstream port. Therefore, the valve 42, preferably a shuttlevalve as illustrated herein, maintains fluid communication between thefluid expansion reservoir 40 and which ever of the first 44 and second46 ports is acting as the downstream port at the time. That is, thevalve 42 is configured to respond to a pressure differential within thehydraulic system and maintains fluid communication between the fluidexpansion reservoir 40 and the low-pressure side of the pump 20. Itshould be noted the while the valve 42 is preferably a shuttle valve,the use of any suitable valve configuration is within the scope of thepresent invention.

FIG. 7 illustrates the fluid flow during an expansion stroke of thehydraulic linear actuator 8. As mentioned above, the amount of fluiddisplaced from the cylinder on this side of the piston is insufficientto fill the hydraulic volume of the cylinder on the other side of thepiston. Therefore, the shuttle valve 42 is positioned to allow fluid toflow from the fluid expansion reservoir 40 into the main flow stream 48of the hydraulic circuit, on the downstream side of the pump 20. In thiscase, port 44 is acting as the downstream port.

FIG. 8 illustrates the fluid flow during a retraction stroke of thehydraulic linear actuator 8. Here, the amount of fluid displaced fromthe cylinder is more than is required to fill the hydraulic volume ofthe cylinder on the other side of the piston. Therefore, the shuttlevalve 42 is positioned to allow fluid to flow from the main flow stream48 of the hydraulic circuit into the fluid expansion reservoir 40, onthe downstream side of the pump 20. In this case, port 46 is acting asthe downstream port.

It will be appreciated that in a preferred embodiment of the presentinvention, the fluid expansion reservoir 40 is closed, that is, notvented, thereby maintaining the hydraulic system as a closed system.Optionally, the fluid expansion reservoir 40 may be pressurized,preferably to a pressure of 2 atmospheres.

Another optional feature of the present invention is the deployment of aflywheel 80 associated with the drive motor 4 as is known in the artwhen using a device that rotates in a single direction at asubstantially constant velocity. This provides the system of the presentinvention a distinct energy usage advantage over systems usingbi-directional drive motors in which a flywheel would be counterproductive.

It will be appreciated that the above descriptions are intended only toserve as examples and that many other embodiments are possible withinthe spirit and the scope of the present invention.

1. A self-contained hydraulic actuator system comprising; (a) a drivemotor configured to rotate at a substantially constant velocity; (b) ahydraulic pump driven by said drive motor; (c) a hydraulic linearactuator in fluid communication with said hydraulic pump so as to beactuated in a first direction by a forward flow state and in a seconddirection by a reverse flow state; (d) a control system associated withsaid hydraulic pump, said control system configured to controladjustment of said hydraulic pump between said forward flow state, anon-flow state and said reverse flow state, and said control systemincludes a bi-directional motor such that a speed and direction of saidadjustment is affected by said bi-directional motor; and (e) apositioning system configures to provide positional informationregarding said hydraulic linear actuator.
 2. The self-containedhydraulic actuator system of claim 1, wherein said hydraulic pumpincludes a controllably variable pumping assembly such that saidadjustments includes a variation of said controllably variable pumpingassembly.
 3. The self-contained hydraulic actuator system of claim 1,wherein said hydraulic pump includes a stator and a rotor deployedwithin said stator and said variation of said controllably variablepumping assembly includes adjusting a positional relationship betweensaid stator and said rotor.
 4. The self-contained hydraulic actuatorsystem of claim 2, wherein said hydraulic pump is a vane pump.
 5. Theself-contained hydraulic actuator system of claim 1, wherein saidpositioning system includes a position feedback system configured toprovide position information regarding said hydraulic linear actuator.6. The self-contained hydraulic actuator system of claim 4, wherein saidposition feedback system includes at least one of an optical encoder anda linear potentiometer associated with said actuator.
 7. Theself-contained hydraulic actuator system of claim 1, wherein said fluidcommunication between said hydraulic pump and said actuator is via aclosed hydraulic system.
 8. The self-contained hydraulic actuator systemof claim 6, further including: (a) a fluid expansion reservoir; and (b)a valve configuration configured so as to maintain fluid communicationbetween said fluid expansion reservoir and a downstream port of saidhydraulic pump.
 9. The hydraulic actuator system of claim 7, whereinsaid hydraulic pump is configured with first and second ports, and saidfirst and second ports alternately act as upstream and downstream portssuch that when said first port acts as said upstream port said secondport acts as said downstream port, and when said first port acts as saiddownstream port said second port acts as said upstream port, therefore,said valve configuration maintains said fluid communication between saidfluid expansion reservoir and one of said first and second ports,dependent on which of said first and second ports is acting as saiddownstream port.
 10. The hydraulic actuator system of claim 7, whereinsaid fluid expansion reservoir is not vented.